This application is based on Application No. 2000-363014, filed in Japan on Nov. 11, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a vehicle surroundings monitoring apparatus which is capable of detecting objects such as vehicles lying in the surroundings of a vehicle of concern, and which is usable with such a device as an intervehicle (vehicle to vehicle) distance warning device, an intervehicle distance control device, a backside warning device or the like, for generating a warning or controlling the vehicle of concern based on the distance of the vehicle of concern to other vehicles lying around the vehicle of concern. More specifically, the present invention relates to such a vehicle surroundings monitoring apparatus which can exhibit the utmost effect particularly in the case of using an optical radar or a laser radar with high sensitivity and a wide horizontal viewing angle.
2. Description of the Related Art
In the past, for a preventive safety device for a vehicle, there has been proposed an intervehicle distance warning apparatus which is mounted on a vehicle of concern (hereinafter simply referred to as a subject vehicle) for measuring the distances from the subject vehicle to other vehicles, particularly to a vehicle running ahead thereof (hereinafter simply referred to as an intervehicle distance) and generate a warning to the operator of the subject vehicle when the intervehicle distance becomes dangerous, i.e., below a prescribed distance. Also, there has been proposed an intervehicle distance control apparatus which adjusts the running speed of a subject vehicle in an automatic manner so as to prevent the intervehicle distance to a vehicle running ahead thereof from becoming shorter than a prescribed value. In these apparatuses, a vehicle surroundings monitoring apparatus using a scanning type laser radar has often been employed for measuring the intervehicle distance and the relative speed of the subject vehicle to the speed of a preceding vehicle running ahead thereof, which is the rate of change of the intervehicle distance.
The scanning type laser radar scanningly irradiates a transmission wave or laser beam over a prescribed angle around the subject vehicle, detects the returned wave or beam reflected by surrounding objects, and measures the distance from the subject vehicle to each object in each radiation direction based on a time span between a transmission time point, at which the transmission wave or beam was irradiated, and a detection time point, at which the reflected wave or beam was received. Therefore, in order to detect surrounding objects, it is necessary to calculate the relative positions and the relative speeds of these objects with respect to the subject vehicle after the objects such as vehicles and obstacles are reconstructed in a measurement space on the basis of the distance data measured in the respective radiation directions. Such a kind of conventional apparatuses are described, for example, in Japanese Patent Application Laid-Open No. 5-180933 and Japanese Patent Application Laid-Open No. 7-318652.
With the apparatus described in the Japanese Patent Application Laid-Open No. 5-180933, an obstacle is first recognized as a set of blocks each of which has a predetermined area based on the detection results of the reflected wave, and the position of the center of gravity thereof is then detected. Subsequently, the position at which the center of gravity of the obstacle is expected to be detected at the next scanning is estimated, and when the center of gravity of the obstacle recognized as the set of blocks is actually detected at the estimated position at the next scanning, it is determined that both of the obstacles actually detected and estimated are the same object. Thereafter, the relative speed of the vehicle to the obstacle is calculated from the rate or amount of change and the difference in time of the positional data of the center of gravity of the obstacles which have been determined to be the same object.
However, since in such a kind of apparatus, an obstacle is recognized as a set of blocks each having a prescribed area, a large amount of information is required to define one obstacle, thus complicating the processing of data. Therefore, the load of a processing device such as a computer has increased. Moreover, since roadside objects such as guardrails are recognized as obstacles, the load of the processing device has further increased in the case where these roadside object exist. Therefore, with these apparatuses, it has been impossible to improve the processing speed and accuracy in the obstacle recognition to any satisfactory extent.
In view of these circumstances, the Japanese Patent Application Laid-Open No. 7-318652 proposes to achieve the detection of surrounding objects according to the following procedure.
1) An obstacle around a subject vehicle is recognized as points.
2) Adjoining ones of the recognized points are combined or integrated with each other into sets of points.
3) Among the integrated sets of points, those sets each of which has a longitudinal length less than a prescribed value in the longitudinal direction of the subject vehicle are recognized as line segments each having a length only in the widthwise direction of the subject vehicle.
4) That position of each of the line segments recognized at a past scanning which is to be expected at the current scanning is estimated, and if the line segment currently recognized is located at the estimated position, it is determined that the past recognized line segment is the same as the current recognized line segment.
5) The relative speed between the subject vehicle and the obstacle is calculated from the positional data of the line segments which are determined to be the same one.
In this manner, the amount of information necessary to define one obstacle is reduced so as to prevent roadside objects such as guardrails from being recognized as obstacles.
However, the conventional apparatuses as described above are based on the following specifications as their premise.
a) A horizontal viewing angle is set to about 16 degrees in order to detect vehicles or obstacles present on a lane on which the subject vehicle is running.
b) Major objects to be detected are highly reflective elements such as reflectors mounted on the rear end of a vehicle, delineators installed on the shoulders of a road, or the like.
Therefore, in the case where a scanning type laser radar is used which is so sensitive as to be able to detect the body of a vehicle and has so wide a horizontal viewing angle as to able to detect vehicles running on lanes adjacent the lane on which the subject vehicle is running in order to improve the detection rate or efficiency or detect an interrupting vehicle, there will arise the following problems with the conventional apparatus, for example, as set forth in the Japanese Patent Application Laid-Open No. 7-318652, thus making such an application difficult.
A) Since the method for determining that the line segment recognized at a past scanning is the same as the line segment recognized at the current scanning is complicated, the number of line segments to be detected increases as the sensitivity and the horizontal viewing angle increase, so the number of combinations of the line segments for determining the same line segment increases accordingly, thereby requiring quite a lot of processing time. That is, the increasing number of detected line segments makes it difficult to perform the recognition processing at a prescribed period or interval.
B) Also, in actually constructing such an apparatus, it is necessary to estimate the maximum amount of processing at the time when the number of segments is increased, in order to determine the capacity of processing required of the apparatus, but with the conventional apparatus, all the possible combinations of line segments must be conceived and examined, and hence it becomes extremely difficult to estimate the maximum amount of processing. Therefore, it is impossible to ensure that the recognition processing can be done at the prescribed cycle under all situations.
The present invention is intended to obviate the above-described problems in the prior art and propose a novel and improved method for detecting and/or tracking an object or objects with a substantially constant amount of processing even if the number of detection points data increases while limiting the maximum processing time.
The object of the present invention is to provide a vehicle surroundings monitoring apparatus using in particular a scanning type laser radar with a high sensitivity and a wide horizontal viewing angle, or using a radio wave radar with a wide viewing angle and a high angular resolution which will be put into practical use in the future.
Bearing the above object in mind, a vehicle surroundings monitoring apparatus according to a first aspect of the present invention includes: a radar for scanningly irradiating electromagnetic waves over a predetermined angular range around a subject vehicle on which the apparatus is mounted, detecting the electromagnetic waves reflected from objects lying around the subject vehicle, and outputting a plurality of directions of scanning irradiation and detected distances from the subject vehicle to the objects in the respective directions of scanning irradiation; and a recognition unit for outputting, based on the detection results of the radar, a relative position and a relative speed, or a rate of change of the relative position, of each of the objects lying around the subject vehicle with respect to the subject vehicle. The recognition unit comprises: a detection points data storage section for storing therein whether or not detection points data in the form of a data pair comprising a direction of scanning irradiation and a detected distance in that direction output by the radar exists in each of Mxc3x97N small regions into which X, Y coordinates with an X axis being set in a widthwise direction of the subject vehicle and a Y axis being set in a running direction of the subject vehicle are divided, in a two-dimensional array including a plurality of elements corresponding to the small regions, respectively; and an object detection section for performing arithmetic operations of multiplication and summation of the respective elements of the two-dimensional array representative of the presence or absence of the detection points data stored in the detection points data storage section while sequentially scanning a mask of a two-dimensional array comprising Jxc3x97K (J less than N, K less than M) elements, and determining, based on the results of the arithmetic operations, attributes such as positions, sizes, etc., of the objects lying around the subject vehicle.
In a preferred form of the first aspect of the present invention, the detection points data storage section comprises: a stop detection points determiner for determining, by the use of information about the subject vehicle, whether each of the detection points data is a piece of stop detection points data representative of the data of a stop or stationary object detected, or a piece of moving points detection data representative of an object other than the stationary object, i.e., a moving object; a stop detection points data storage section for storing, based on the results of determination of the stop detection points determiner, the presence or absence of stop detection points data in each of Mxc3x97N small regions into which X, Y coordinates with an X axis being set in a widthwise direction of the subject vehicle and a Y axis being set in a running direction of the subject vehicle are divided, in a two-dimensional array comprising a plurality of elements corresponding to the small regions, respectively; and a moving detection points data storage section for storing, based on the results of determination of the stop detection points determiner, the presence or absence of moving detection points data in each of the Mxc3x97N small regions into which X, Y coordinates with an X axis being set in a widthwise direction of the subject vehicle and a Y axis being set in a running direction of the subject vehicle are divided, in a two-dimensional array comprising a plurality of elements corresponding to the small regions, respectively. The object detection section comprises: a stationary object detector for performing arithmetic operations of multiplication and summation of the respective elements of the two-dimensional array representative of the presence or absence of the stop detection points data stored in the stop detection points data storage section while sequentially scanning a mask of a two-dimensional array comprising Jxc3x97K (J less than N, K less than M) elements, and determining, based on the results of the arithmetic operations, attributes such as positions, sizes, etc., of stationary objects lying around the subject vehicle; and a moving object detector for performing arithmetic operations of multiplication and summation of the respective elements of the two-dimensional array representative of the presence or absence of the moving detection points data stored in the moving detection points data storage section while sequentially scanning a mask of a two-dimensional array comprising Jxc3x97K (J less than N, K less than M) elements, and determining, based on the results of the arithmetic operations, attributes such as positions, sizes, etc., of moving objects lying around the subject vehicle.
In another preferred form of the first aspect of the present invention, the recognition section further comprises a column detection points determiner for determining whether the respective detection points data are column detection points data representative of data arranged in the running direction of the subject vehicle, and the detection points data storage section does not use the column detection points data in its processing.
In a further preferred form of the first aspect of the present invention, the recognition section further comprises a column detection points determiner for determining whether the respective detection points data are column detection points data representative of data arranged in the running direction of the subject vehicle, and the stop detection points data storage section or the moving detection points data storage section does not use the column detection points data in their processing.
In a yet further preferred form of the first aspect of the present invention, the recognition unit further comprises a curved road detection points determiner for determining whether the respective detection points data are curved road detection points data representative of data arranged along a curved road, and the detection points data storage section does not use the curved road detection points data in its processing.
In a still further preferred form of the first aspect of the present invention, the recognition unit further comprises a curved road detection points determiner for determining whether the respective detection points data are curved road detection points data representative of data arranged along a curved road, and the stop detection points data storage section or the moving detection points data storage section does not use the curved road detection points data in their processing.
A vehicle surroundings monitoring apparatus according to a second aspect of the present invention comprises: a radar for scanningly irradiating electromagnetic waves over a predetermined angular range around a subject vehicle on which the apparatus is mounted, detecting the electromagnetic waves reflected from objects lying around the subject vehicle, and outputting detected distances from the subject vehicle to the objects lying around the subject vehicle and directions of the objects from the subject vehicle; and a recognition unit for outputting, based on the detection results of the radar, a relative position and a relative speed, or a rate of change of the relative position, of each of the objects lying around the subject vehicle with respect to the subject vehicle. The recognition unit comprises: an object detection section for detecting positions of the objects by using detection points data obtained by the radar, and calculating object positional data representative of the positional data of the objects; an object position estimator for estimating a position of each object detected in the past which should currently be detected, based on the past positional data of that object; a window setter for setting a prescribed window in such a manner as to surround the estimated position of each object output by the object position estimator; and an object tracker for determining the current positional data of an object by using the detection points data contained in the window set by the window setter, and calculating a relative speed of that object to the subject vehicle by using the positional data of that object detected in the past.
In a preferred form of the second aspect of the present invention, the recognition unit further comprises a stop detection points determiner for determining, by the use of information about the subject vehicle, whether each of the detection points data is a piece of stop detection points data representative of the data of a stopped object detected, or a piece of moving points detection data representative of an object other than a stopped object, and the object tracker calculates, based on the determination results of the stop detection points determiner, a current positional data of an object, by using the stop detection points data contained in the window set by the window setter when a difference between a relative speed of that object with respect to the subject vehicle detected in the past and a speed of the subject vehicle detected in the past is less than a prescribed value, but by using the moving detection points data contained in the set window when a difference between a relative speed of that object with respect to the subject vehicle and a speed of the subject vehicle both detected in the past is equal to or greater than the prescribed value, and the object tracker also calculates a current relative speed of that object with respect to the subject vehicle by using the current and past positional data of that object.
In another preferred form of the second aspect of the present invention, the object detection section does not use the detection points data which were used to calculate the object positional data in the current processing of the object tracker.
In a further preferred form of the second aspect of the present invention, the recognition section further comprises a column detection points determiner for determining whether the respective detection points data are column detection points data representative of data arranged in the running direction of the subject vehicle, and the object tracker does not use the column detection points data in its processing based on the detection results of the column detection points determiner.
In a yet further preferred form of the second aspect of the present invention, the recognition unit further comprises a curved road detection points determiner for determining whether the respective detection points data are curved road detection points data representative of data arranged along a curved road, and the object tracker does not use the curved road detection points data in its processing based on the detection results of the curved road detection points determiner.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of a preferred embodiment of the present invention taken in conjunction with the accompanying drawings.